1. Field of the Invention
The present invention relates to a process for preparing a half-vanadocene compound and more particularly to a process for preparing a half-vanadocene compound in a high yield using a chemically stable vanadocene compound as a starting material.
2. Description of Related Art
A half-vanadocene compound, typically vanadium complex of cyclopentadiene, is widely used as a catalyst for polymerization of olefins or diolefins. The half-vanadocene compound exhibits a high activity as a catalyst for polymerization of butadiene, and is an important catalyst which is indispensable in organic synthesis.
Examples of the half-vanadocene compound include (C5H5)VOCl2, (C5H5)VCl3 and the like. A number of processes are known for preparing such half-vanadocene compounds.
It was reported to prepare (C5H5)VOCl2 by reacting (C5H5)V(CO)4 with a mixed gas of oxygen and chlorine (J. Organomet. Chem., No. 319, page C21 (1987)). Further reported was a process for preparing (C5H5)VOCl2 by reacting(C5H5)V(CO)4 with oxygen and SOCl2 (Z. Naturforsch., B: Chem. Sci., No. 53, p. 153 (1998)).
However, these processes pose problems. If purified (C5H5)V(CO)4 is not used as the starting material, the contemplated compound can not be produced with a high purity in a high yield. Further these processes are not practical in other respects. (C5H5)V(CO)4 used as the starting material is likely to decompose, and a large amount of toxic carbon monoxide is required in preparation of the compound. Moreover, a large amount of toxic carbon monoxide is produced in chlorination of (C5H5)V(CO)4.
A process was reported for preparing (C5H5)VOCl2 by reacting (C5H5)2V with (CH3)3COOH to give (C5H5)VO2 and treating the obtained compound with SOCl2. (Tr. Khim. Khim. Tekhnol., Vol. 4, p. 32 (1974)). This process necessitates separation and removal of by-products in the cause of the reaction so that the reaction involves a prolonged reaction procedure for conversion of an industrial raw material VCl4 to (C5H5)VOCl2. Thus the process is not practical.
Japanese Unexamined Patent Publications No. 298191/1998 and No. 130779/1999 disclose processes for preparing(C5H5)VOCl2 by reacting VOCl3 with (C5H5)MgCl. However, the (C5H5)VOCl2 is produced in a yield of as low as 25%. Thus the disclosed processes are not practical.
Also reported was a process for preparing (C5H5)VCl3 which comprises reacting (C5H5)V(CO)4 with SOCl2 (Z. Anorg. Allg. Chem., No. 423, p. 231 (1976)). This process needs (C5H5)V(CO)4 as the raw material and is not practical.
The above-mentioned publication also discloses a process for preparing(C5H5)VCl3 which comprises treating (C5H5)2VCl2 with SOCl2. However, when purified (C5H5)2VCl2 is not used as the raw material, a high-purity (C5H5)VCl3 would not be produced in a high yield.
As described above, prior art processes for preparing a half-vanadocene compound are not practical in that the starting compound is likely to decompose and a half-vanadocene compound can not be produced in a sufficiently high yield.